KR100482174B1 - Fabrication Method of GaN related LED using Substrate Remove Technology - Google Patents

Abstract

The present invention relates to the fabrication of GaN-based LEDs of a novel structure to improve low external quantum efficiency, thermal problems and non-uniform current distribution problems in the active layer of the conventional AlGaInN-based LEDs. The most unique feature of this proposed structure is to remove the substrates (Al ₂ O ₃ , SiC, Si ...) used for the growth of GaN-based LED thin film, and to the N-doped GaN thin film revealed by the substrate removal. It is a method of manufacturing an LED by forming an N-metal and attaching it to a silicon substrate so that the P-metal part is a junction. The advantage of this structure is that by eliminating the substrate, it solves the problem of light loss at the interface due to the difference in dielectric constant between the substrate and GaN and absorption of light output by the substrate, and also with LED thickness thinned below 10um. Therefore, Photon Recycling can be effectively performed inside the LED device to improve the external quantum efficiency, and heat generated from the LED can easily escape to the silicon substrate through the P-metal. The thermal properties can be greatly improved. In addition, it is possible to greatly improve the current non-uniform distribution in the active layer of the device due to the low P-doping problem of the GaN-based LED, local P-metal formation and N-metal formation problem.

In the present invention, GaN-based LED having a PN junction diode structure, after forming a P- metal on the front surface of the P-doped thin film, the substrate is inverted and bonded to the silicon (Si) substrate so that the P-metal junctions After the removal of the substrate using the method proposed in the present invention, the N-doped GaN thin film revealed by the formation of the N-metal formed by the LED is characterized in that the fabrication.

Description

Fabrication Method of GaN related LED using Substrate Remove Technology}

The present invention relates to a method of manufacturing a GaN-based LED of a novel structure to significantly improve the light output, thermal characteristics and current uniformity of the active layer of the conventional GaN-based LED (Light Emitting Diode).

In general, a GaN-based LED (Light Emitting Diode) is a buffer layer (11), N-type GaN layer 12, InGaN (on the substrate 10, such as a sapphire substrate, as shown in the accompanying drawings Or a GaN) active layer 13, a P-type GaN layer 14, a transparent electrode 15, a dielectric protective film 16, an N-type metal electrode 17 and a P-type metal electrode 18, the sapphire The buffer layer 11, the N-type GaN layer 12, the InGaN (or GaN) active layer 13, and the P-type GaN layer 14 on the substrate 10 are sequentially disposed in accordance with the MOCVD (Metal Organic Chemical Vapor Deposition) method. After crystal growth, a portion of the N-type metal electrode 17 is etched to form the N-type GaN layer 12, a transparent electrode 15 is formed as necessary, and then except for the electrode region. The portion is covered with the dielectric protective film 16 and formed by depositing the N-type metal electrode 17 and the P-type metal electrode 18.

Light generated by the combination of electrons and holes in the active layer is emitted into the air through the transparent electrode. In this light emission process, half of the light generated in the active layer proceeds to the substrate side (opposite to the light emitting surface), and a large amount of light is lost due to the dielectric constant difference between GaN and the substrate and the absorption effect on the substrate. . In addition, due to the thick substrate, it is difficult to expect a large photon recycling effect inside the LED device. In general, the photorecycling effect is that a large part of the light generated in the active layer is trapped inside the LED device due to the difference in dielectric constant between the device and the surroundings. Regeneration or, for some reason, the effect of some or all of the trapped light being released into the air.

As is well known in the conventional LED structure as shown in FIG. 1, localized P, N-metal formation, and low P-doped concentration cause a problem of non-uniformity of current in the LED active layer, resulting in non-uniformity of output light. Distribution problems are caused. In addition, conventional LEDs have poor thermal conductivity, such as sapphire, because they are bonded to the package mounter, resulting in poor device and thermal characteristics due to poor thermal conductivity of the existing substrates (Al ₂ O ₃ , SiC, ...). There is. This problem will seriously affect the device's performance as the device's operating current increases.

Therefore, in order to improve the performance of GaN-based LED, it is absolutely necessary to improve the above-mentioned problems.

The present invention has been made to solve the above problems, an object of the present invention is to remove the substrate on which the GaN-based LED is grown to eliminate the light absorption loss by the substrate and the loss due to the dielectric constant difference between the GaN material and the substrate In addition, by maximizing the Photon Recycling effect in the device, it improves the external quantum efficiency, and also forms N-metal on N-GaN thin film exposed by substrate removal, and P-doped side The purpose of the present invention is to improve the uniformity of the current by depositing P-metal on the entire surface of the device, and to improve the thermal characteristics of the device by bonding the P-metal side of the device to a silicon substrate having excellent thermal conductivity.

An important technical task to achieve this effect is the technique of removing the substrate used for thin film growth. The present invention solves this technical problem to provide a GaN-based LED manufacturing method of a new structure.

In order to achieve the above object, the method of N-metal formation on N-doped thin film revealed by adhesion of LED thin film and silicon substrate, removal of substrate used for LED thin film growth and removal of substrate is characterized.

Preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2 shows the structure of a thin film grown for a conventional GaN-based LED. The buffer layer 21, the N-GaN layer 22, the InGaN / GaN / AlGaN active layer, the barrier layer 23, and the P-GaN layer 24 are sequentially formed on the substrate 20. Holes supplied from P-GaN and electrons supplied from N-GaN are combined in the active layer, so that energy is transformed into light by the current, thereby generating light having a wavelength corresponding to the energy band gap of the material.

3 is a view after depositing the existing P-metal 30 (Ni / Au, Ti / Au, Cr / Au, etc.) on the grown LED thin film. Finally, the P-metal thus formed forms a P-electrode in the LED device. The P-metal pattern between each unit LED element is spaced 31 as shown in FIG. 3 for etching between the elements and finally cutting each LED element. This interval can be from 0.1um to 500um.

FIG. 4 shows a conventional dry etching method (RIE, RIBE, ICP, etc.) or wet etching method (UV assisted KOH etching, etc.) between the elements 31 using the formed P-metal as a masking material for etching. Etch to the appropriate depth of the N-GaN 22 or less buffer (21). Then, to protect the surface of the device, the etched surface is protected by using a dielectric such as SiNx and SiOx. The dielectric protective film 41 thus formed and the groove 40 between the elements formed by etching are shown in FIG. 4, respectively. The grooves thus formed play several very important roles in the process for removing the substrate. First, when the substrate is removed by using a mechanical method, a lot of stress is transferred to the LED thin film. This stress is absorbed by the groove to minimize the damage of the device due to stress. Secondly, a strong strain is formed between the grown LED thin film and the substrate due to the severe mismatch of lattice constant, which minimizes the damage of the device by mitigating it by using the groove formed in the previous. The third groove 40 is an important index indicating the degree of etching when the substrate is removed using a mechanical method or another method. In other words, when the etching is performed to a sufficient depth, the groove 40 is exposed to the surface being etched, so that the etching is sufficiently performed, indicating that the N-GaN or lower layer is exposed on the surface.

FIG. 5 shows a substrate on which the LED devices described in FIG. 4 are fabricated, and a conductive adhesive (e.g., a highly conductive silicon 51 on which metals are deposited on both sides of a similar size, or a highly conductive silicon 51 on which metals are not deposited). Using a conventional flip-chip bonding technique using a material such as a conductive adhesive epoxy (50) or an indium bump, the cross-section of the P-metal surface is shown after the adhesive is turned upside down. Giving. Here, the purpose of inverting the LED substrate on which the devices are fabricated on the silicon substrate is that the silicon substrate serves as a mounter of the LED thin film when the substrate on which the LED device is manufactured is supported, and supports an LED device having a thickness of about 10 um. It serves to prevent the damage. In addition, since the silicon substrate has excellent thermal conductivity, it serves as a heat sink that effectively dissipates heat generated inside the LED.

6 is a cross-sectional view after removing a substrate on which an LED is formed by a conventional mechanical grinding and polishing method or a wet to dry etching (ICP, RIE, etc.) method or a mixture thereof. have. As mentioned above, in this process, the groove formed in FIG. 4 is exposed to the surface, which indicates that the substrate is sufficiently etched. This groove also absorbs the stresses between the elements, protecting the elements from various stresses.

7 shows a cross section after forming N-metal 70 (Ti / Au, Ni / Au, Cr / Au, etc.) on the exposed N-GaN surface. N-metal can be formed around the edges of the device or in the middle of the device. Here, the portion where the N-metal is not formed becomes the light output window. In general, in GaN-based LEDs, N-doping can achieve much higher doping concentration than P-doping, and ohmic formation with metal is very easy. Therefore, P-gly is formed on the entire surface of P-GaN as shown in the figure. The structure of forming N-metal in the local portion of N-GaN becomes a very easy structure for the uniformity of current in the active layer.

FIG. 8 is a cross-sectional view of one LED device after cutting the devices finally formed in FIG. 7. A GaN-based LED is attached to the silicon substrate 51, and the LED device includes a P-metal 30, a P-GaN layer 24, an active layer and a barrier layer 23, and an N-GaN layer on which light is emitted. 22), the dielectric protective film 41 and the N-metal 70 are formed.

Another Example

Another embodiment in which the electrostatic discharge (ESD) problem of the device may be significantly solved will be described with reference to the accompanying drawings. In the present invention, a large area PN diode is integrated in the reverse direction of the LED device by using an AlGaInN-based LED having a P-metal formed thereon and a silicon substrate having a PN junction formed when the P-metal portion is bonded to the silicon substrate. This can easily solve the problem of electrostatic discharge (ESD) of the device. In general, although AlGaInN-based LED is a material with a large energy band gap, the quality of the grown thin film is relatively poor compared to other materials, and thus, is generally vulnerable to ESD. In general, AlGaInN-based LEDs are about 300V-1000V in the forward direction and 100V-1000V in the reverse direction. This is because there is a large electric field between the P-N junctions of the LEDs at the reverse voltage. In order to solve this problem, in general, the PN diode is connected in the reverse direction to the LED so that when the voltage is reversed, the PN diode is operated so that the turn-on voltage of the PN diode connected in parallel to the LED device. Only the low voltage corresponding to reverses protects the device from ESD. The conventional method for this is to form a PN diode by partially doping on one side of the silicon and attaching the LED to the silicon substrate where the PN junction is made using the flip-chip technology of the semiconductor. Build an LED module. However, the problem with this method is a complicated process that requires a PN junction on one side of the silicon, and the LED chip must also be integrated into the silicon PN diode using flip-chip technology, which requires sophistication. As a result, the manufacturing process is complicated, the yield is disadvantageous.

Another embodiment of the present invention is devised to improve the above problems, and another object of the present invention is to attach a silicon diode in which a PN junction is formed perpendicularly to the bottom of the P-metal of the GaN-based LED, in parallel with the LED. The present invention provides a semiconductor device and a method of manufacturing the same, which dramatically improves the ESD problem of LEDs by connecting the silicon PN diodes in the reverse direction.

As shown in FIG. 9, a silicon P-N diode having a P-N junction in a vertical direction is used instead of the silicon substrate shown in FIG. 8. In this silicon PN diode, a PN junction can be formed by doping a P-dopant to an N-doped silicon substrate, and a PN junction can be formed by doping an N-dopant to a P-doped silicon substrate. . The P and N-electrodes are formed by depositing P and N-Ohmic metals on the silicon P-N diode thus formed. If necessary, it may be used without forming one or all of the electrodes. In FIG. 9, 90 represents an N-doped silicon substrate or an N-doped silicon layer, and 91 represents a P-doped silicon layer or a P-doped silicon substrate. And 92 and 93 represent N and P-metal, respectively. A single LED chip incorporating a silicon P-N diode is attached over a typical LED package mounter to form wire bonding 96. The P-metal 93 of the silicon PN diode is bonded to the N-electrode 94 side of the LED package mounter and wire-bonded from the N metal electrode 92 of the silicon PN diode to the P-electrode 95 of the LED package mounter. (Wire Bonding) 96 is formed. Then, a wire bonding 96 is formed from the N-metal 70 of the LED to the N-electrode 94 of the LED package mounter.

9 shows a circuit configuration diagram of the LED module shown in FIG. 9. The circuit connection between GaN-based LED and large-area silicon P-N diode is shown in reverse.

According to the present invention made as described above, by removing the substrate used for LED thin film growth can eliminate the light loss due to the difference in dielectric constant between the GaN-based thin film and the substrate, and can eliminate the light loss due to light absorption by the substrate Will be. In addition, by removing the substrate, the LED device becomes very thin, around 10um, thereby increasing the Photon Recycling effect in the device, thereby finally improving the external quantum efficiency.

In addition, in the present invention, since the existing silicon substrate known to have very good thermal conductivity is used as a mount of the device, the heat generated from the LED can be effectively removed, thereby improving the life and electrical characteristics of the device. There is this.

In addition, in the present invention, since the P-metal is deposited on the entire surface of the P-GaN, which is generally known to be difficult to do high concentrations, it is possible to reduce the serial resistance of the device, and also partially N on the N-GaN surface having excellent electrical conductivity. -Formation of metal and light output window greatly improves the uniformity of current density in active layer. This makes it possible to obtain a uniform light output over the entire light output surface of the LED element.

In another embodiment, in the case of LEDs in which silicon PN diodes are reversely integrated, silicon PN diodes are reversely integrated in AlGaInN-based LED devices having low reverse ESD voltages, thereby dramatically improving reverse ESD voltage performance, thereby improving reliability of AlGaInN LED devices. Can be greatly improved. Compared with the conventional silicon PN diode deposition method, a sophisticated flip-chip process is not required for the integration process, and the silicon PN diode is also very easy to fabricate since it uses a large area of silicon PN diode formed vertically. . The biggest advantage of the present invention compared to the conventional method is that the integration process of the silicon P-N diode is very simple, and thereby the device fabrication yield can be greatly improved.

1 is a general structure of a conventional GaN-based LED device.

2 is a cross-sectional view showing a thin film structure grown for manufacturing a conventional GaN-based LED (Light Emitting Diode).

3 is a cross-sectional view after depositing a P-metal on P-GaN.

4 is a cross-sectional view after etching the formed P-metal to a predetermined depth of the N-doped GaN thin film to form grooves of a suitable depth and protecting the etched surface using a dielectric.

FIG. 5 is a cross-sectional view of the LED fabricated up to FIG. 7 after being inverted with the P-metal side bonded to the silicon substrate. FIG.

6 is a cross-sectional view after removing the substrate on which the LED is grown using a mechanical method or a dry or wet etching technique.

7 is a cross-sectional view after forming an N-metal in the N-GaN layer exposed by substrate removal.

8 is a cross-sectional view of a single LED device finally made according to the present invention.

FIG. 9 is a cross-sectional view of an LED device in which a silicon P-N diode is integrated into an LED according to another embodiment of the present invention. FIG.

<Description of the code | symbol about the principal part of drawing>

20. Substrate 21. Buffer Layer

22.N-GaN layer 23.InGaN / GaN / AlGaN active and barrier layer

24.P-GaN layer 30.P-metal

40. Grooves formed by etching 41. Surface protection dielectric.

50. High Conductivity Silicon Substrate 51. Conductive Adhesive

70. N-metal 90. N-doped silicon layer or substrate

91. P-doped silicon layer or substrate. 92.N-Omic Metal

93. P-Omic Metal 94. N-electrode of Package Mounter

95. P-electrode of package mounter 96. Wire bonded metal

Claims (9)

In the GaN-based LED thin film having a P-N junction diode structure, Depositing P-metal on the P-GaN layer of the LED thin film; Etching the P-metal to an N-GaN or buffer layer by a masking process to form grooves for device isolation; Bonding the P-metal of the LED thin film to a highly conductive silicon substrate; Removing the growth substrate of the LED thin film; And And forming an N-metal on the N-GaN surface exposed by the growth substrate removal. The method of claim 1, wherein the etching width is 0.1 μm to 500 μm during dry or wet etching for device isolation. The substrate of claim 1, wherein the highly conductive silicon substrate has a N or P-doping concentration in a range of 10 ¹⁵ to 10 ²² , with or without an ohmic metal formed on both sides or a cross section. GaN-based LED manufacturing method using the removal technology. The method of claim 1, wherein the growth substrate is removed by mechanical etching, dry etching, wet etching, or a combination thereof. The light output window of claim 1, wherein an N-metal such as Ti / Au, Ni / Au, Cr / Au is formed at an edge portion or a center portion of the N-GaN layer so that an N-metal is not formed. GaN-based LED manufacturing method using a substrate removal technology characterized in that. In the GaN-based LED thin film having a P-N junction diode structure, Depositing P-metal on the P-GaN layer of the LED thin film; Etching the P-metal to an N-GaN or buffer layer by a masking process to form grooves for device isolation; Bonding the P-metal of the LED thin film to the N-metal of the silicon diode substrate having a P-N junction in a vertical direction; Removing the growth substrate of the LED thin film; Fabricating an LED device by depositing N-metal on the N-GaN surface exposed by removing the growth substrate; Bonding the P-electrode of the silicon P-N diode substrate of the LED device to the N-electrode of the LED package mounter; And Wire bonding from the N-metal of the silicon P-N diode substrate to the P-electrode of the LED package mounter, and wire bonding from the N-metal of the LED to the N-electrode of the LED package mounter. GaN LED manufacturing method using substrate removal technology. The method of claim 6, wherein the thickness of the P-doped layer and the N-doped layer of the silicon P-N diode substrate is 0.01um to 1mm, respectively. The silicon PN diode substrate of claim 6, wherein the silicon PN diode substrate forms a PN junction by P-doped N-doped silicon substrate or a PN junction by N-doped P-doped silicon substrate, and the P-doped silicon substrate. And a concentration of N-doped is in the range of 10 ¹⁵ to 10 ²² GaN-based LED manufacturing method using a substrate removal technology. The method of claim 6, wherein the silicon P-N diode substrate is formed of an ohmic metal on one or both surfaces thereof.